As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of batteries has also sharply increased as an energy source for the mobile devices. Also, much research on batteries satisfying various needs has been carried out.
In terms of the shape of the batteries, the demand of prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for the batteries, the demand of lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having high energy density, high discharge voltage, and high output stability, is very high.
FIG. 1 is an exploded perspective view typically illustrating the general structure of a conventional pouch-shaped secondary battery.
Referring to FIG. 1, a pouch-shaped secondary battery 100 includes an electrode assembly 300, electrode taps 310 and 320 extending from the electrode assembly 300, electrode leads 410 and 420 welded to the electrode taps 310 and 320, respectively, and a battery case 200 for receiving the electrode assembly 300.
The electrode assembly 300 is a power generating element comprising cathodes and anodes successively stacked one on another while separators are disposed between the respective cathodes and anodes. The electrode assembly 300 is constructed in a stacking structure or a stacking/folding structure. The electrode taps 310 and 320 extend from corresponding electrode plates of the electrode assembly 300. The electrode leads 410 and 420 are electrically connected to the pluralities of electrode taps 310 and 320 extending from the respective electrode plates of the electrode assembly 300, for example, by welding. The electrode leads 410 and 420 are partially exposed to the outside of the battery case 200. To the upper and lower surfaces of the electrode leads 410 and 420 is partially attached insulative film 430 for improving sealability between the battery case 200 and the electrode leads 410 and 420 and, at the same time, for accomplishing electrical isolation between the battery case 200 and the electrode leads 410 and 420.
The battery case 200 is made of an aluminum laminate sheet. The battery case 200 has a space for receiving the electrode assembly 300. The battery case 200 is formed generally in the shape of a pouch. In the case that the electrode assembly 300 is a stacking type electrode assembly as shown in FIG. 1, the inner upper end of the battery case 200 is spaced apart from the electrode assembly 300 such that the plurality of anode taps 310 and the plurality of cathode taps 320 can be coupled to the electrode leads 410 and 420, respectively.
In the pouch-shaped secondary battery 100 with the above-stated construction, the electrode assembly 300 is mounted in the battery case, which has low mechanical strength. As a result, there is much possibility that the pouch-shaped secondary battery 100 is easily deformed when external impacts are applied to the battery or the battery drops, and short circuits occur inside the battery when the battery is deformed. Especially, the lower-end corners of the battery case 200 are weak, and therefore, when strong impacts are applied to the lower-end corners of the battery case 200 or the battery drops with any one of the lower-end corners of the battery case 200 down, there is further increased the possibility that short circuits occur inside the battery.
Consequently, the demand of a technology for preventing abrupt flow of electric current and catching fire or explosion of the battery due to short circuits occurring inside the battery as a result of the penetration of a needle-shaped body into the battery, which frequently occurs, as well as the dropping and vibration of the battery, and more efficiently securing the safety of the battery is very high.